Considerable danger of accidents exists with power saws or power chain saws which are guided by hand at the two handles thereof. Recoil and kick-back movements can arise when working with such a saw as a result of suddenly encountered obstructions. These kick-backs can cause severe injury when the cutting tool, i.e. the saw chain in the case of a chain saw, is not immediately brought to a standstill. The danger of accident is especially great if one or both of the handles is released accidentally or even on purpose, because the saw then no longer can be safely guided. Consequently, different safety devices are known for such power saws. With the safety device disclosed in U.S. Pat. No. 3,793,727--Moore issued Feb. 26, 1974, a friction brake is associated with the drive sprocket or chain wheel of the saw chain. This friction brake is kept inoperative by means of a stop, which comprises several members of a linkage, so long as each of two levers which are coupled with the linkage is grasped at the same time as the two handles. When even one of the two handles is released, the lever associated therewith is pivoted and hence the stop is released, as a result of which the friction brake passes into its operating position under the effect of a pressure spring, and the saw chain is braked or stopped.
The continuous actuation of both levers by the linkage against the force of the pressure spring is tiring. Also, while working with the saw, the brake can be tightened or actuated without external cause, i.e. unnecessarily, if one of the handles is temporarily not tightly or firmly held. Additionally, the arrangement of the linkage requires an accurate adjustment and frequent servicing with readjustments, since the members of the linkage can become bent.